This snapshot was taken at the slit-lamp microscope when checking the pressure of a patient’s eye. The Goldman tonometer is a circular prism that is pushed against the surface of the cornea. You can see the Fleuroscein circles (the yellow semi-circles) on either side of the horizontal devide.
The correct pressure is obtained when you adjust tension such that these circles “touch” each other. This picture may not make much sense, so I recommend you watch the applanation mires video that this snapshot was taken from.
Goldman tonometry like works off the Imbert Fick principle: which says that an external force excerted agains a sphere (the eyeball) equals the pressure witin the sphere (the IOP we want) times the area of the cornea flattened. Don’t worry too much about the mathematics … just realize that our equipment is designed such that if we can flatten a circular area of the cornea that is exactly 3.06mm in diameter, then we can calculate out what the internal pressure is inside the eye.
The applanator has an internal prism that is designed such that when the two hemicircles of fleurosceine touch, you know your flattening a perfect 3mm diameter circle of corneal surface.
Comments and Feedback
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Thank you sooo much for taking the time of making and posting the videos, they are SOOOO VERY HELPFUL..THanK YOU THANK YOU THANK YOU
Comment by Gloria — January 18, 2011 @ 2:16 pm
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